Electrical power for vehicles, including automobiles, trucks and buses, is typically supplied by alternator-battery systems. The alternator is usually driven by mechanical means to generate electric power. The power output of the alternator is controlled by a voltage regulator, which senses the voltage output of the alternator and adjusts the alternator magnetic field or rectification control to maintain a desired value of alternator output voltage.
The electrical power for the vehicles may be used in heavy duty, high current applications, such as operating vehicular air conditioning. In such applications, a single alternator may not produce sufficient electric power. To generate additional power, two or more alternators may be connected in parallel when the total system electrical load exceeds the power generating capacity of a single alternator.
If two or more alternators are required in a system, each alternator typically has its own voltage regulator. The voltage control is therefore performed independently for each alternator. In this instance, even if the multiple alternators are identical in every respect, there remain different voltages present in the system due to variety of factors. One factor is different voltages present in the system due to cabling and connection voltage drops that change with electrical load. For example, an alternator's location within the system requires interconnecting cabling and connectors that may affect the voltage at the alternator's output. Another factor is differences in alternator performances. For example, an alternator's performance may be affected by its operating temperature. Temperature variations in the system may result in the alternators operating at different temperatures, thereby resulting in different alternator outputs. These temperature variations may be due to internal or external cooling airflow dynamics or the proximity to nearby sources of heating or cooling.
As a result, when load changes occur, the portion of the total electrical load supplied by each alternator is not predicable or constant. Rather, the instability of the system is manifested by unstable output voltages and unbalanced distribution of electrical load as load changes occur. This instability is a condition called “hunting” and is caused by the portion of the total load supplied by each individual alternator not being constant. Another undesirable effect of the instability is that one alternator in the system assumes most, or potentially all, of the total system load. In such cases the overworked alternator may suffer premature failure.
Solutions to the problem of multiple alternators have been attempted. One such attempt is disclosed in U.S. Pat. No. 5,723,972 (Bartol et al.) in which two or more alternators are electrically connected in parallel across a battery and load. A corresponding number of electronic voltage regulators individually control the alternators, with one regulator that is specially configured as the master and the other regulators are configured as followers to receive a signal from the master regulator. The master regulator only senses the voltage across the battery and generates a master control signal for use in both the master regulator and all follower regulators to generate the power to the electric loads and maintain regulated voltage.
What is needed is better inter-regulator control of multiple alternators.